Stream Terraform output through web interface (take 2)

[schultzor]

I took the existing work from this PR #1315 and updated it against the current main branch. I also added plumbing for a ParallelCommand type through the various interfaces for keeping track of commands that are invoked in parallel vs those invoked serially (currently this is only used for adding a command prefix on the webconsole output).

I went ahead and opened a new PR for this since the previous one was marked as unmaintained, apologies if that was the wrong approach here 🙇

[nishkrishnan]

Hey @schultzor we're already working on a version from this inspired from the original PR with a couple modifications. We'll be testing this in production as well to make sure that it can handle a reasonable scale before patching it upstream.

[fblgit]

We did a patch for this time back, and u must consider these:

1. Housekeeping: the SQLite is not a "performance" DB.. u don't want it to be large.
2. When the plan is applied, the web interface entry disappears so you will have to keep them, but how many? for how long?
3. If you store the plans in the DB, the UI becomes very slow in the long term due to the size of the DB. Even if you only leave the entries and u have the output of the plan in a static file.. it becomes slow when u have 100 plans stored.
4. Pagination
5. WebServer performance degradation, noticeable, after 200~ plans.